Storage tube with collectorbackplate unitary target



Nov. 3, 1964 J. c. FIRMIN 3,155,869

STORAGE TUBE. WITH COLLECTOR-BACKPLATE UNITARY TARGET Filed Feb. '7, 1961 gun, and a the cathode of the writing United States Patent 3,155,869 STORAGE TUBE WETH COLLEQTGR- BACKPLATE UNETARY TARGET ilervois Campbell Firmin, Little Baddovv, England, as-

signor to English Electric Valve Company, London, England, a British company Filed Feb. 7, 1961, Ser. No. $7,625 Claims priority, application Great Britain, Feb.

5,294/60 6 Claims. (Cl. 2315-12) This invention relates to signal storage arrangements and more particularly to such arrangements of the kind employing signal storage tubes of the so-called bi-stable or black and white type, i.e. tubes in which the stored information is representative of either signal or no signal conditions but is not representative of other signal variations such as signal amplitude.

Signal storage arrangements in accordance with the present invention may, although this is not a necessity, employ electron discharge storage tubes of present known construction. Nevertheless, as will be seen later, arrangements in accordance with this invention are such that the discharge tubes used therein do not operate in the usual known manner.

According to this invention a signal storage arrangement of the kind referred to comprises an electron discharge tube having a fluorescent screen, a storage electrode arranged parallel to and spaced from said screen, said storage electrode comprising a metallic grid or mesh having deposited thereon, on the side remote from said screen, a layer of insulating material, a writing electron flood electron gun; means for applying to gun and said screen high potentials which are negative and positive, respectively, in relation to the flood gun cathode potential; means for stabilising the potential of said insulating layer at the flood gun cathode potential; means for subsequently applying to said metallic grid or mesh a potential which, in relation to the flood gun cathode potential, is positive and of a value exceeding the so-called first secondary emission crossover of said insulating layer; and means for switching on said writing gun in correspondence with signals to be stored, the whole arrangement being such that in operation the storage electrode insulating layer is stabilised,.before Writing, substantially at the potential of the flood gun cathode, and during writing and storage the storage electrode metallic grid or mesh is held at said potential exceeding the insulating layer first secondary emission crossover whereby portions of said layer bombarded by the electron beam from said 15, lass,

writing gun will increase in potential and will be stabilised at substantially the potential of said metallic grid or mesh, and whereby electrons from said flood gun pass through the storage electrode at said bombarded portions and impinge on said fluorescent screen. 1

Preferably the axis of the writing gun is perpendicular to the surface of said storage electrode.

Preferably the tube has a further grid or mesh arranged parallel to but spaced from the storage electrode on the side thereof remote from the fluorescent screen, and means are provided for applying thereto a potential of such value that in operation the further grid or mesh will collect gas ions.

The storage electrode grid or mesh may conveniently be a woven grid or mesh.

The invention is illustrated in and further described with reference to the accompanying drawing, the single figure of which shows, in simplified diagrammatic form one embodiment thereof.

Referring to the drawing the discharge tube therein shown has an envelope 1, on one end face of which is deposited a fluorescent screen 2, shown as a thickened line,

3,155,859 Patented Nov. 3, 1964 having a metal backing film (not separately shown) in accordance with usual known practice. Parallel to the screen 2 and spaced at small distance therefrom is a storage electrode 3 comprising a metallic grid or mesh having deposited thereon, on the side remote from the fluorescent screen, a layer of insulating material which lies only on the wires of the metallic grid or mesh and does not fill its interstices. Spaced from the storage electrode on the side remote from the fluorescent screen is an ion collecting electrode in the form of a metallic mesh or grid 4.

The discharge tube has two electron guns, a writing gun 5 arranged on the axis of the storage electrode 3 and a flood gun 6 arranged at an angle to the storage electrode axis. Each of these electron guns may be constructed in well known manner, the writing gun 5 being arranged to produce a Writing electron beam which may be switched on or off in accordance with. signals applied thereto, and the flood gun 6 being arranged to produce a continuous flooding electron beam which is substantially equally distributed over the surface of the storage electrode 3.

Each of the electrodes 2, 3 and 4 and the cathodes of each of the two electron guns are connected to suitable sources of potential which are indicated conventionally in the drawing as comprising the batteries '7 and 8 and the potentiometers 9 and 1d. The arrangement is such that, regarding the flood gun cathode as at earth or zero volts, the writing gun cathode is at a large negative potential, the fluorescent screen 2 is at a large positive potential, the ion collecting grid or mesh 4 at such a potential, which will depend on other operating conditions, as to collect ions satisfactorily and the metallic grid or mesh of the storage electrode 3 at a potential, which is varied in a manner and to an extent which will be described hereinafter, between zero and at least twice the potential corresponding to the so-called. first secondary emission crossover of the insulating layer of the storage electrode.

Typical figures for the potentials of the various electrodes are shown in the drawing. Such figures are given by Way of example only and are in no way limiting.

In operation, the flooding beam, i.e. the electron beam from the flood gun 6, is continuously on and initially the storage electrode grid is held at zero potential, with the Writing beam, i.e. the electron beam from the writing gun 5 cut off. Under the influence of the flooding beam the storage electrode insulator is stabilised at the cathode potential of the flood gun, i.e. at zero volts, and the storage electrode grid is then increased in potential to a value slightly in excess of the first secondary emission crossover of the storage electrode insulator, the rate of increase of potential being sufl iciently slow that the insulator remains at zero potential and does not in crease in potential due to its capacitative relationship with the metallic grid.

The writing gun is now switched on in accordance with signals to be stored and displayed and is deflected by suitable means (not shown) across the storage electrode in known manner. The voltage of the writing beam is arranged to be such that the secondary electron emission from the insulator of the storage target, in response to the impinging Writing beam, will cause those parts of the insulator struck by the writing beam to increase in potential despite the effect of the flooding beam. If the potential reached by the bombarded parts of the insulator exceeds the first secondary emission crossover then the potential of those parts will become stabilized, due to the action of the flooding beam, at the potential of the storage electrode metallic grid or mesh, which acts as the secondary electron collector. Any part of the insulator, however, which, although bombarded by the writing beam, does not reach the first more stabilized at the flood gun cathode potential.

stored.

3 crossverpotential will rapidly return as zero potential under the influence of the flooding beam. This might occur, for example, on the fringes of the area bombarded by the writing beam. It should be noted that the potentialsof the-storage electrode grid and the ion collecting grid, spaced from the storage electrode, are all such that the potential at which the storage electrode insulator is stabilized is substantially independent of the ion collecting grid potential.

When the writing beam is switched ofl the storage electrode insulator now carries a positive charge pattern corresponding to the applied signals and the flooding beam is enabled to pass through the interstices of the storage electrode at the positively charged areas and strike the fluorescent screen, with increased velocity so producing a pattern thereon representative of the applied signals. As will be clear, the charge pattern on the storage electrode will remain substantially unchanged for so long as the flooding beam and the potential of the metallic grid of the storage electrode remain unchanged.

To erase the stored charge pattern the potential of the metallic grid of the storage electrode may be raised in potential by an amount in excess of the first crossover potential of the storage electrode insulator and at suflicient speed to ensure that the surface of the insulator increases likewise in' potential due to the capacitative relationship between it and the metallic grid. The Whole of the storage electrode surface is now stabilized at a positive potential and the Whole of the fluorescent screen is activated by the flooding beam. The potential of the 7 storage electrode grid is now reduced to zero, the potential of the insulator consequently decreases and is once Alternatively, erasure may be carried out by merely decreasingthe storage electrode grid potential to zero and increasing it again to a potential in excess of the first crossover.

It will be noted that in the illustrated arrangements the Writing beam axis is perpendicular to the storage target. This arrangement, although not a necessity, is advantageous as it allows the fidelity of storage and reproductions to be increased. This arrangement of the writing gun is possible due to the fact that the'arrangements in accordance with the present invention, unlike many known arrangements, do not require that the flooding beam be projected perpendicular to the storage electrode as the small variations in the storage electrode insulator potential due to the lack of normal incidence of the flooding beam are negligible compared with the dilference in potential between the charged and uncharged 'parts of the insulator.

This lack of sensitivity of the storage tube to small variations in the insulator potential also permits the metallic grid of the storage electrode to be a woven grid.

I claim:

1.,A bistable signal storage arrangement comprising an electron discharge tube having a fluorescent screen, a storage electrode arranged parallel toiand spaced from said screen, said storage electrode comprising a metallic grid having a layer of insulating material deposited thereon on the side remote from said screen, a writing electron gun and a flood electron gun, means for operating said flood gun to provide a continuous flooding electron beam, a reference point having the potential of the flood gun cathode, a source of potential having a value with respect to the flood gun cathode potential between the first and second secondary emission cross-overs of said layer, means for connecting said grid during signal storage to said source, means for applying potentials to the cathode of said writing gun and said screen which are negative and positive respectively in relation to the flood gun cathode potential and means for switiching on said writing gun in correspondence with signals to be 2. An arrangement as-claimed in claim '1 wherein the tube has a further grid arranged parallel to but spaced from the storage electrode on the side thereon remote ,from the fluorescent screen, and means are provided for 4. A method of operating a bistable signal storage tube having a fluorescent screen, a storage electrode ar ranged parallel to and spaced from said screen, said storage electrode comprising a metallic gridhaving a layer of insulating material deposited thereon on the side remote from said screen, a Writing electron gun and a flood electron gun, said method including the steps of causing said flood gun .to provide a continuous flooding electronbeam, applying a high potential to said screen, stabilizing said layer at flood gun cathode potential, subsequently applying to the grid. during signal storagea potential between the first and second secondary emission cross-overs of said layer, with respect to the flood gun cathode potential, switching on the Writing gun in correspondence with signals thereby to stabilize at the potential of the grid portions of said layer bombarded by the writing beam and cause flood beam electrons at said bombarded portions to pass through the grid and impinge on said screen.

5. A bistable signal storing arrangement comprising an electron discharge tube having a fluorescent screen, a storage electrode arranged parallel to and spaced from said screen, said storage electrode comprising a metallic grid having a layer of insulating material deposited thereon on the side remote from said screen, a Writing electron gun, and a flood electron gun; means for operating said flood gun to provide a continuous flooding electron beam; a circuit point of reference potential; means for maintaining the flood gun cathode at said reference potential; means, including a source of potential having'a value between the first and second secondary, emission crossovers of said layer, for causing said gridto collect secondary electrons emitted by said layer during. signal storage; means for applying potentials tothe cathode. of said writing gunv and to said. screen which are negative and positive, respectively, in relation to said reference potential; and means for switching on said writing gun in correspondence with signals to be stored.

6. A bistable signal storage arrangement comprising an electron discharge tube having a fluorescent screen, a storage electrode arranged parallel to and spaced from said screen, said storage electrode comprising a metallic gridhaving a layer of insulating material deposited thereon on the side remote from said screen, a writing electron gun, and a flood electron gun; means for operating said flood gun to provide a continuous flooding electron beam; a circuit point of reference potential; means for maintaining the flood gun cathode at said reference po tential; means for initially connecting said grid prior to signal storage to said circuit point; a source of potential having a value between the first. and secondsecondary emission cross-overs of said layer; means for subsequently connecting said grid during signal storage to said source to collect secondary electrons emitted by said layer at said grid; means for applying potentials to the cathode of said Writing gun and to said screen which are. negative and positive, respectively, in relation to said reference potential; and means for switching on said writing gun in correspondence with signals to be stored.

References Cited in the fileof this patent UNITED STATES PATENTS 

1. A BISTABLE SIGNAL STORAGE ARRANGEMENT COMPRISING AN ELECTRON DISCHARGE TUBE HAVING A FLUORESCENT SCREEN, A STORAGE ELECTRODE ARRANGED PARALLEL TO AND SPACED FROM SAID SCREEN, SAID STORAGE ELECTRODE COMPRISING A METALLIC GRID HAVING A LAYER OF INSULATING MATERIAL DEPOSITED THEREON ON THE SIDE REMOTE FROM SAID SCREEN, A WRITING ELECTRON GUN AND A FLOOD ELECTRON GUN, MEANS FOR OPERATING SAID FLOOD GUN TO PROVIDE A CONTINUOUS FLOODING ELECTRON BEAM, A REFERENCE POINT HAVING THE POTENTIAL OF THE FLOOD GUN CATHODE, A SOURCE OF POTENTIAL HAVING A VALUE WITH RESPECT TO THE FLOOD GUN CATHODE POTENTIAL BETWEEN THE FIRST AND SECOND SECONDARY EMISSION CROSS-OVERS OF SAID LAYER, MEANS FOR CONNECTING SAID GRID DURING SIGNAL STORAGE TO SAID SOURCE, MEANS FOR APPLYING POTENTIALS TO THE CATHODE OF SAID WRITING GUN AND SAID SCREEN WHICH ARE NEGATIVE AND POSITIVE RESPECTIVELY IN RELATION TO THE FLOOD GUN CATHODE POTENTIAL AND MEANS FOR SWITCHING ON SAID WRITING GUN IN CORRESPONDENCE WITH SIGNALS TO BE STORED. 